Fix /dashboard/adjust/remove/ PHP 8.1 strlen(null) errors
/dashboard/adjust/remove/ POST requests fail under PHP 8.1 with strlen(null) errors.
This change fixes it.
View a dashboard which has some panels. Eg https://my.phorge.site/dashboard/view/1/
Click on a 'Manage Panel' dropdown and click on 'Remove Panel'
Confirm the panel is removed and no strlen(null) errors are generated.
Reviewers: O1 Blessed Committers, avivey
Reviewed By: O1 Blessed Committers, avivey
Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15549
Differential Revision: https://we.phorge.it/D25345